This application claims priority to German Application No. 10231143.9, which was filed in the German language on Jul. 10, 2002.
The present invention relates to a method for controlling the valve lift of discretely adjustable inlet valves in a multi-cylinder internal combustion engine, the operation of which is regulated by an electrical operation control unit.
Internal combustion engines with inlet valves, the valve lift of which can be adjusted between a low and high value, in other words discretely, for example using an adjustment mechanism, are increasingly being used in motor vehicles, for example see DE 195 20 117 and MTZ Motortechnische Zeitschrift 61 (2000), 11, p. 730-743. On switching over the valve lift, the air mass in the cylinders as well as the volume of injected fuel undergo a sudden change, which causes a correspondingly sudden change in the torque, unless the torque is suppressed via a regulating operation. An option for suppressing these sudden changes in torque is by operating the cylinders at a reduced level of efficiency, for instance by adjusting the ignition angle, directly after a valve lift switchover, for example from a lower to a higher value, thus decreasing the excess torque that is created when the valve lift switches over. However, such a switchover strategy would be at the expense of increased fuel consumption.
In one embodiment of the present invention, there is a method for controlling the valve lift of discretely adjustable inlet valves in a multi-cylinder internal combustion engine, permitting a valve lift switchover which consumes as little fuel as possible at a torque which is as regular as possible.
In one aspect according to the invention, the valve lift is firstly adjusted for a section of cylinders, while the remaining section of cylinders is adjusted after a delay.
In doing so, it is possible for the valve lift to be adjusted for each individual cylinder or in groups of cylinders in succession. However, it is preferable for the valve lift to be adjusted firstly for half the cylinders and then for the other half. In each case, it is important to note that the valve lift for the first section of cylinders is adjusted in such a way that combustion in each cylinder in the first section of cylinders takes place alternately with combustion in a cylinder in the second section of cylinders.
By switching the valve lift over in stages as proposed according to the invention, only a small change in torque occurs each time during the switchover processes, which can be compensated with greater ease and more efficient consumption via a corresponding regulating control operation. The respective change in torque which would arise if no regulating control operation took place during the switchover processes is expediently compensated by changing the efficiency of at least some of the cylinders. The change in efficiency is preferably achieved by changing the ignition angle for the cylinders in question. Another option for compensating the change in torque is to change the air/fuel ratio. It is also possible to combine both options.
When the valve lift is adjusted for the first section of cylinders, the throttle valve mounted in the intake tract of the internal combustion engine is expediently adjusted in such that the pressure in the intake tract moves toward a target value, at which all cylinders operate again at optimum efficiency once the valve lift has been switched over.
Once the valve lift has been adjusted for the first section of cylinders, the regulating control by the electronic operation control unit ensures that the cylinders return to operating at optimum efficiency, e.g. with a base ignition angle and/or an air/fuel ratio of one. The valve lift for the second section of cylinders is to be adjusted at this point at the latest.
If the change in torque occurring with a valve lift adjustment without any additional regulating control operation is compensated by adjusting the ignition angle, the case may arise under specific operating conditions in which the ignition angle adjustment required to avoid a sudden change in torque is so large that the minimum ignition angle would have to be undershot. However, as the regulating control by the operation control unit restricts the ignition angle to the minimum ignition angle, a sudden change in torque would nevertheless occur in this case.
According to another aspect of the present invention, a criterion is specified for the option of switching valve lift over at neutral torque. If this criterion shows that it is not possible to switch valve lift over at neutral torque with a required valve lift switchover, there will either be no valve lift switchover at this point or a valve lift adjustment will take place for a reduced number of cylinders.